Three enzymes in myelin and cells from the nervous system are the subject of the proposed studies. One enzyme, carbonic anhydrase, occurs in other subcellular fractions as well as in the myelin sheath. This enzyme will be purified from myelin and characterized and will also be measured in oligodendroglial plasma membranes and isolated axolemma, two membrane systems which are likely to be associated with myelin fractions. Because carbonic anhydrase is believed to take part in regulation of intracellular ions and water in the brain and is considered, on the basis of somewhat ambiguous data, to be a "glial" marker enzyme, its activity will be studied in detail also in isolated astrocytes, neurons, oligodendroglia and axons. The carbonic anhydrase in choroid plexus will be studied with reference to participation in ion and fluid transport into the cerebrospinal fluid. The second enzyme, 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP), is considered a marker enzyme for myelin. Although loss of CNP activity occurs during demyelination, the function of CNP remains unknown. We will explore under new conditions the hypothesis that CNP has ribonuclease activity, and will also attempt to inhibit the enzyme in vitro and in vivo in an effort to determine whether loss of CNP activity prevents myelination or results in demyelination. We have found a third enzyme, 5'-nucleotidase, in myelin. Although this enzyme is almost as highly enriched in myelin as is CNP, 5'-nucleotidase is also found in other plasma membranes and probably participates in the transport of adenosine, which is believed to be a neurotransmitter. We will determine the distribution of 5'-nucleotidase, as well as the other two enzymes, in neurons, astrocytes and oligodendroglia during development.